This application relates generally to optical systems, and more particularly to techniques and devices for mounting optical devices.
In virtually any optomechanical engineering application, it is necessary for optical elements to be mounted within the system with accurate alignment. This is especially the case for a variety of high-performance optical systems, such as may be used in fiber-optic telecommunications applications, among others. In the design and manufacture of such systems, optical components are typically mounted with a lens cell, with the optical axis of such optical components being aligned with respect to an axis of the lens cell. The lens cell may then be used within an assembly having multiple components, the alignment of the optical elements within the assembly being achieved through alignment of the lens-cell axis.
Examples of such a prior-art lens cell are illustrated in FIGS. 1A-1F. FIG. 1A shows a perspective drawing of a prior-art lens cell 100 in which optical elements are positioned within the lens cell 100. FIGS. 1B and 1C respectively show a cutaway perspective drawing and a cross-sectional projection drawing of the same lens cell 100 in which other features of the lens cell 100 may be more apparent. An external cylindrically shaped body 104 is used to house the optical elements, which in FIGS. 1A-1C are shown as a pair of achromatic lens doublets 120 and 124 separated by a spacer 116. The spacer 116 forms part of the interior of the lens cell 100 and is used for configurations in which a separation is desired between individual lens elements. The optical elements 120 and 124 are configured such that they share a common optical axis that is coincident with the central axis 102 of the cylindrical external body 104.
The optical elements 120 and 124 are mounted within the lens cell 100 on their outside diameters, requiring machining of tight tolerances. The interior of the lens cell may be configured with different inside diameters at different points in order to accommodate differences in optical elements. For example, the lens cell illustrated in FIGS. 1A-1C is configured generally with an inside diameter ID(1) that is appropriate for housing the first lens doublet 120. It also includes a notched portion with a larger inside diameter ID(2) at that point where the second lens doublet is mounted. After machining the lens cell 100 with tight tolerances, the optical elements are typically mounted within by filling any small space around a given lens element with an elastomeric material such as a room-temperature vulcanizing elastomer. The optical elements are additionally secured with a threaded retainer clamp 128, which is secured within the lens cell 100 by threads 132 and perhaps also by staking. For the illustrated prior-art configuration, at least one end of the lens cell 100 is equipped with a shoulder 112 having a plurality of notches 108 that may assist in maintaining alignment of optical elements when the lens cell 100 is integrally connected with a subsequent component of the optical-system assembly.
FIGS. 1D, 1E, and 1F show cross-sectional details of different optical elements that may be mounted. In these figures, reference numerals correspond generally to those structures in FIGS. 1A-1C, but include primes to designate structures that may be configured differently to accommodate differences in the optical elements.
In FIG. 1D, for example, a plano-concave lens 120xe2x80x2 having flat surfaces is shown. The external body 104xe2x80x2 provides a holding structure for the lens 120xe2x80x2 having surfaces S1xe2x80x2 and S2xe2x80x2 in a nominally aligned condition relative to the axis 102 of the lens cell. The flat surfaces of the lens 120xe2x80x2 are configured in contact with seat 134xe2x80x2 and the retainer clamp 128xe2x80x2. In FIG. 1E, an example of an optical element having only a single flat surface, in this instance a plano-convex lens 120xe2x80x3 having surfaces S1xe2x80x3 and S2xe2x80x3, is shown. The lens 120xe2x80x3 is mounted similarly to the external body 104xe2x80x3, with the plano surface of the lens configured in contact with the seat 134xe2x80x3, but a precision centering spacer 136xe2x80x3 is additionally installed over the outer convex optical surface in contact with the retainer clamp 128xe2x80x3. In FIG. 1F, a meniscus lens 120xe2x80x2xe2x80x3 having surfaces S1xe2x80x2xe2x80x3 and S2xe2x80x2xe2x80x3 is shown. Although the lens 120xe2x80x2xe2x80x3 has two curved surfaces, it includes a sag 156xe2x80x2xe2x80x3 configured for contact with a precision centering spacer 136xe2x80x2xe2x80x3. The lens 120xe2x80x2xe2x80x3 is mounted to the external body 104xe2x80x2xe2x80x3 by including a conical or spherical surface 158xe2x80x2xe2x80x3 used to center the lens 120xe2x80x2xe2x80x3 to the cell and by including a retainer clamp 128xe2x80x2xe2x80x3.
Such prior-art lens-cell arrangements suffer from a number of disadvantages, including the need to satisfy tight tolerances to mount the optical elements on their outside diameters. Generally, the outside diameter of the lens must be controlled to the optical axis as well as the sag. The difficulty in achieving proper alignment is evident for all three of the mounting schemes shown in FIGS. 1D-1F. In general, the axis 152 of the lens 120 may be tilted with respect to the axis 102 of the lens cell 100 by an angle xcfx86 and may be offset longitudinally by a distance xcex94z; in the figures, axis 150 shows the lens axis 152 after being rotated to be parallel to the cell axis 102. Mounting of the lens 120 seeks to achieve (xcfx86=xcex94z=0.
Thus, with the arrangement of FIG. 1D, the tilt xcfx86 of the lens axis 152 is established by the shoulder in contact with the seat 134xe2x80x2 and by alignment of S1xe2x80x2 and S2xe2x80x2. Centration of lens 120xe2x80x2 is established by the low-precision threaded retainer clamp 128xe2x80x2. The arrangement of FIG. 1E is somewhat better. The precision centering spacer 136xe2x80x3 is match-machined for mating to the inside diameter of the lens 120xe2x80x3. Centration of the lens 120xe2x80x3 to the cell 100 is therefore established by the carefully machined conical surface of the spacer 136xe2x80x3. The tilt is controlled the same fashion as in FIG. 1D. In the arrangement of FIG. 1F, in which the lens 120xe2x80x2xe2x80x3 includes sag 156xe2x80x2xe2x80x3, both the tilt and centration are controlled by the precision spacer 136xe2x80x2xe2x80x3.
For these prior-art designs to be effective, it is necessary to control a number of physical parameters to very great precision, including: (i) the inside diameter of the external body 104; (ii) the relative sizes of the outside and inside diameters of the external body 104; (iii) the position of the conical or spherical seat position relative to the external body 104; (iv) the outside diameter of the spacer 136 relative to the outside diameter of the external body 104; (v) the orientation of the spacer 136 relative to the outside external body 104; and (vi) the orientation of the lens sag 156 to the lens axis 152. A deficiency in any one of these parameters may result in a poorly oriented lens in the lens cell. Accordingly, it is desirable to have another lens-cell arrangement that avoids these disadvantages.
Thus, embodiments of the invention are directed to an apparatus and method for housing an optical element. In one embodiment, a first optical component is configured with a ring having a symmetry that corresponds to that of the optical element. The ring is configured for bonding with the optical element on an optical surface at a periphery of the optical element.
In certain embodiments, the invention is directed to an optical-system assembly that includes the first optical component engaged with a second optical component. The first optical element may include a means for demountably engaging the ring with another component of the optical-system assembly. The second optical component includes a base and a plurality of engagement members connected with the base for engagement with the ring.
In certain embodiments, the ring is further configured for bonding with a second optical element on an optical surface at a periphery of the second optical element. The ring may thus be configured to act as a spacer separating the two optical elements along a symmetry axis of the ring. The symmetry axis of the ring may be coincident with optical axes of each of the two optical elements. In some embodiments, at least one of the two optical elements comprises a lens doublet.
In certain embodiments, three notched structures are provided on an exterior side of the ring. Each notched structure may comprise a groove that extends radially from the ring. In some embodiments, the groove has a triangular cross section and in others has a cross section shaped as a gothic arch. The engagement members may comprise spheres that are configured to fit each such groove. The first and second optical components of the optical-system assembly may be secured with an axial retaining spring. The axial retaining spring includes a body that has a symmetry axis corresponding to a common symmetry of the first and second optical components. It also includes a plurality of axial constraint fingers extending from the body substantially parallel to the symmetry axis and configured to engage the second optical component. A plurality of structures on the body are adapted to apply a point load at selected locations on the first optical component.
In one embodiment, the optical-system assembly is incorporated in a wavelength router. The wavelength router receives light having a plurality of spectral bands at an input port and directs subsets of the spectral bands to output ports. A free-space optical train disposed between the input port and the output ports provides optical paths for routing the spectral bands. The optical train includes the first and second optical components, with the first optical component including a lens element and the second optical component including a dispersive element. The router also includes a routing mechanism that has at least one dynamically configurable routing element. A given spectral band may be directed to different output ports depending on a state of the dynamically configurable routing element.